A hygrometer that measures humidity based on the changes in the length of a human hair as it absorbs and desorbs moisture. Hair is hygroscopic and when mounted under tension, it expands and contracts with changes in relative humidity. One end of a set of hair strands is fixed and the other is used to control a pointing device or a recording pen. Hair hygrometers work well over the relative humidity range of 20-100%. However, the changes are slow and the response lag time increases at cooler temperatures. Hair hygrometers are relatively inexpensive, but should be calibrated every two to three months with a psychrometer.
Synonyms and Related Terms
Haarhygrometer (Deut.), Fadenhygrometer (Deut.); hygromètre à cheveu (Fr.); higrómetro de cabelo (Port.)